1. Field of the Invention
The present invention relates to a zoom lens system, particularly to such system having a function to stabilize a blurred image when a camera is handheld during low shutter speeds and used in low light levels.
2. Description of the Related Art
In conventional photography, the quality of photographs was often deteriorated mainly because of out of focus and camera-shake.
Recently, an auto-focus mechanism has been employed in a camera. In addition, the auto-focus mechanism performs to a high degree of accuracy. Therefore, the problem caused by out of focus has been almost solved.
On the other hand, the problem caused by camera-shake has not been solved. One reason is that the magnification or the telephoto ratio of a lens system is becoming higher and higher, resulting that an influence of camera-shake on an image becomes great. In addition, a camera, such as a lens shutter camera, equipped with a zoom lens system has taken the place of a camera equipped with a fixed focal length lens system. Furthermore, a zoom lens system having a higher zooming ratio, or a longer focal length range is required recently, in general. Blurred image caused by camera-shake is more serious in such zoom lens system since the caused blur is enlarged.
Relating to camera-shake, various deflecting lens systems to stabilize a blurred image by moving a particular lens portion of the image forming lens system in a perpendicular direction relative to an optical axis have been suggested in Japanese laid open Pats. Nos. 63-115126, 63-118708, 63-133119, 63-229425, 63-201622, 63-201623, 63-169614, 50-137555, 63-201624 and 1-116619, and U.S. Pat. No. 4,907,868.
In addition, a mechanism for moving the deflecting lens portion, which comprises, for example, an acceleration sensor and an actuator, is shown in Japanese laid open Pat. No. 62-47011.
However, these related arts disclose mainly deflecting lens systems to stabilize a blurred image in a fixed focal length lens system.
In using a deflecting lens group stabilizing the blurred image in the zoom lens system, aberrations (asymmetry of field curvature and paraxial comatic aberration) based on decentering of the deflecting lens group must be decreased all over the zooming range. However, even if the deflecting lens system described in the related art is employed in the zoom lens system, it is very difficult to effectively reduce the aberration all over the zooming range. Especially, it is difficult to effectively reduce the aberration, in the center of photographing region, based on decentering of the deflecting lens group.
On the other hand, if a deflecting lens group to stabilize the blurred image is employed in a zoom lens system, it is desirable to correct aberrations caused in the deflecting lens group by the deflecting lens group itself. This means that the number of the lens elements composing the deflecting lens group will be increased, resulting that the entire size of the zoom lens system and a mechanism moving the deflecting lens group will be enlarged.